Aluminum refining



May 21, 1968 Filed Sept. 8, 1965 N. W. F. PHILLIPS ETAL ALUMINUMREFINING 2 Sheets-Sheet l CIRCULATOR Some Al Fog SomeAlClm700C lmpure lAl at 675C 24 AICI CONVERTER DECOMPOSER AlCl 38, H

2 Pure Al Al CI 36 |200 c RESIDUE GAS HE AT ER Alcl INVENTORS NORMAN W.EPHILLIPS FREDERICK WILLIAM SOUTHAM BY WS'Mn/a-W ATTORNEY May 21, 1968Filed Sept. 8, 1965 N. W. F. PHILLIPS ET AL ALUMINUM REFINI NG 2Sheets-Sheet lmpure Al l /3 AICI3 200 c 44 42 v l SCRUBBER GIRCULATOR fiA'rsn 40B 56 CIRCULATOR AICI3 Some AICI L Alcl impure N \L SomeAl Fogx Isaw-e Am 61 o m 5 C --58 /4-- 40A CYCLONE SEPARATOR AICI; l0- 5 34DECOMPOSER L 38- Pure Al 32 CONVERTER Pure Al 7 6- 36 200C e- IINVENTORS NORMAN W.F. PHILLIPS FREDERICK WILLIAM SOUTHAM laz utaA-cmnwATTORNEY United States Patent 3,384,475 ALUMINUM REFINING Norman W. F.Phillips and Frederick William Southam,

Arvida, Quebec, Canada, assignors to Aluminium Laboratories Limited,Montreal, Quebec, Canada, a corporation of Canada Filed ept. 8, 1965,Ser. No. 485,862 14 Claims. (Cl. 75-68) This invention relates toimprovements in the refining of aluminum metal by the so-calledsubhalide distillation procedure, and more particularly the presentinvention is concerned with the problems of scrubbing unwantedconstituents from the halide gases employed in the process and withsupplying necessary heat to impure aluminum bearing solid materials usedin the process.

In particular, the present invention is related to improved procedureand apparatus for carrying out the subhalide distillation process forthe refining of aluminum where gaseous normal aluminum halide isemployed to convert aluminum metal from an impure body thereof. Theconversion is to a gaseous aluminum subhalide which is thereafterdecomposed to yield purified metal and a restored quantity of the normalhalide.

In the subhalide process for refining or extracting aluminum, the impurematerial generally consists of alloys of aluminum with other metals orthe like, or other compositions or bodies of aluminum and foreignmaterial, usually metallic, all such mixtures, compositions oraggregates being here generically considered as impure aluminum. In apreferred way of carrying out the refining operation, the impurematerial, in divided solid form, is supplied substantially continuously,e.g. by increments from time to time, into a suitable converter offurnace-like character, where it is heated and where the normal halideof aluminum in gaseous form is passed through it, for example aluminumtrichloride (AlCl or aluminum tribromide (AlBr also commonly calledrespectively aluminum chloride and aluminum bromide. At appropriatetemperature, ordinarily in the range of about 1000 C. and upwards, thegaseous halide reacts with the aluminum in the material to produce, ingaseous form, an aluminum subhalide, e.g. monohalide. Thus theconversion reaction, where the treating gas is aluminum trichloride,yields aluminum monochloride, carrying the aluminum in gaseous combinedform.

The solid material under treatment is thus progressively depleted ofaluminum, e.g. as it moves downward through a converter of verticaltype, so that the resulting aluminum-impoverished solids are dischargedfrom a lower part of the converter. The gas withdrawn from the upperpart of the conversion chamber contains the aluminum subhalide, usuallytogether with unreacted normal halide, and is advanced to anothervessel, which may be called a decomposer, where at suitably lowertemperatures the reverse reaction occurs, with the subhalide revertingto aluminum and normal aluminum halide. The metallic aluminum,conveniently in molten state, is there deposited and collected, whilethe discharged gas now again consists essentially of the normal aluminumhalide, e.g. aluminum trichloride.

However, an equilibrium concentration of aluminum subhalide remains inthe discharged gas dependent upon the discharge temperature andpressure. For instance, when the chlorides are used, an equilibriumconcentration of aluminum monochloride equivalent to approximately fourpounds of aluminum per 10,000 pounds of gas remains in the dischargedgas it the temperature is 700 C. and the pressure is one atmosphere.Furthermore, this discharge gas contains a certain amount of condensedliquid aluminum in extremely finely divided form such 'ice that it issuspended in the discharge gas and may be said to constitute an aluminumfog. These constituents in the gas discharged from the decomposer havebeen found to create some serious problems because they cause corrosiveattack on the metals used in pipe lines and mechanical gas circulatorswhich are used for additional, handling of the gas. Furthermore, duringsuch additional handling, the aluminum fog tends to condense and settleout and solidify and to thus build up blockages in the apparatus.Furthermore, additional circulation generally results in additionalcooling of the gaseous discharge from the decomposer, and this causesfurther decomposition of the residual equilibrium quantity of subhalidegas to release additional pure aluminum.

Accordingly, one important object of the present in vention is to reducethe temperature of the gas discharged from the decomposer and to removethe aluminum condensate fog and the subhalide from the gas while at thesame time avoiding corrosion and blockages due to accumulation ofsolidified aluminum.

In the practice of theprocess of the present invention, substantialquantities of heat must be supplied to the converter in order to achievethe desired reaction in which the normal aluminum halide is converted,at least in part, to the aluminum subhalide. A large amount of this heatmay be supplied by electrical resistance heating, by passing an electriccurrent directly through the impure solid aluminum bearing materialwithin the cohverter. For example, this solid material, in divided orgranular form, may be contained in a refractory-lined converter vesselor furnace having internal electrodes at spaced locations and anelectric current may be caused to flow between these electrodes. Suchconverter or furnace may be of an upright shaft type, with embeddedannular electrodes at vertically spaced localities along the inner wallsand with arrangements for introducing the normal aluminum halide vaporand withdrawing the product gas, for removing spent solid material andfor inserting further quantities of unreacted solids. The solid materialis conveniently prepared in a granular form, which may range from coarsepowder (or fine granules) to relatively large lumps, the extent andcharacter of subdivision being governed by the need for porosity to thegases and for a sufficiently high ratio of the surface area to thevolume of the solid to provide an efiicient rate of removal of aluminum.In the operation of such a converter it has been proposed to introducedthe unreacted halide gas at one end of the body of divided solidmaterial and to withdraw the subhalide-containing gas from a highlyheated zone of the mass, i.e. adjacent the electrode which is furthestfrom the locality of gas entrance, the principle of such operation beingto remove the gas at a zone of maximum heat, for best economy in theseparation of aluminum in subhalide form.

The use of electrical resistance heating to supply heat energy for theendothermic reaction in the converter is regarded as avoidingdifficulties that would be encountered in certain other ways offurnishing heat. For instance, the nature of the reaction precludes theuse of direct firing or other arrangements exposing the material tocombustion or combustion products. External heating, meaning anyprocedure whereby heat is to be conducted through the wall of theconverter or other structure from a localized source, appearsundesirable for providing the relatively considerable flow of heatenergy which the reaction must consume as it progresses. That is to say,with external heating applied to the body of solid fragments, lumps orgranules constituting the charge in the reaction zone, for example withheating means around the converter or even with heating elementsembedded in or otherwise exposed to the charge, it is difficult toobtain the heat transfer rates necessary for a large power input withoutcausing considerable temperature gradients, and it is correspondinglydifiicult to avoid a low thermal etficiency. If there are largetemperature variations between dilferent localities of the charge, thespecial nature of the reaction is such that there will either be placesof undesirably low temperature where there is little conversion ofaluminum to subhalide (or even redeposit of metal from subhalideproduced elsewhere), or if such situation is to be avoided, there willbe some places kept at an excessively and thus wastefully hightemperature, perhaps even to the point of objectionable melting of thematerial.

Although internal resistance heating, with electric current supplied ina manner that would be expected to distribute its flow through thecharge, should obviate the above difliculties, it has been discoveredthat in many cases a correspondingly serious problem arises.Specifically it is found that a highly uneven current distribution oftenoccurs, with large temperature differences, of a random and upredictablesort, among various parts of the charge. It has been discovered thatthese non-uniform current conditions with local overheating and largetemperature gradients, arise in bringing cold charge material up toreaction temperature (as must be done continuously, in a continuousoperation) and also tend to persist after the material has been brought,generally, to reaction temperatures. The condition of uneven heating maybe so severe as to have other adverse effects on the practicalaccomplishment of the reaction, e.g. in that there may be agglomerationof particles or pieces of the charge due to local fusion.

Accordingly, it is another object of the present invention to provide anefficient method for preheating the solid materials prior to theconverter operation in order to avoid the above mentioned difliculties.

Another feature and object of the present invention is to accomplishboth of the above mentioned objects by a single addition step. Thus itis an important feature of the present invention that the gaseousdischarges from the decomposer are used for the purpose of preheatingthe solid aluminum bearing materials which are to be reacted upon in theconverter, and in the process of accomplishing the preheating function,these gases are scrubbed and cleansed of constituents which are notdesired at this stage of the process.

Thus, in carrying out the present invention, the gases discharged fromthe decomposer are passed through a new charge of the divided solidaluminum bearing material so as to preheat that material before it issubjected to the higher temperature reaction of the converter. Anyliquid aluminum fog or residual subhalides remaining in the gaseousdischarge from the decomposer and supplied to the charge of solidaluminum bearing material are substantially completely removed, theentrained metallic aluminum being deposited in this new charge of impurealuminum material.

Another object of the present invention is to pro vide apparatus whichis particularly useful for carrying out subhalide distillation processesfor the recovery of aluminum.

Other objects, advantages and features of the present invention will beapparent from the following description and the accompanying drawingswhich are as follows:

FIG. 1 is a schematic flow chart of a preferred form of the process ofthe present invention. This flow chart illustrates the process in partthrough the use of schematically illustrated system components. Thus,the figure can be considered also as a schematic illustration ofapparatus suitable for carrying out the process.

FIG. 2 is a schematic flow chart illustrating a modification of theprocess illustrated in FIG. 1 and again the process is illustratedpartially in terms of schematic apparatus components, and thus, can betaken also to illus- 4 trate apparatus suitable for carrying out thismodification of the process.

And FIG. 3 illustrates, in somewhat more detail, an actual structurewhich may be employed for the scrubber-preheater function in theprocesses and apparatus of the present invention.

Stated in a more complete form, the improved subhalide distillationprocess for the recovery of aluminum in accordance with the presentinvention may be carried out by following the steps of passing a normalhalide of aluminum in preheated gaseous form through divided solidimpure aluminum bearing material while supplying heat thereto so that atleast a portion of the gaseous halide reacts with the aluminum in thematerial to produce a gaseous aluminum subhalide. The subhalidecontaining gas is then removed and decomposed at a lower temperature toobtain the reverse reaction in which the subhalide reverts to the normalaluminum halide and releases pure aluminum. Then the decomposed gasesare passed through a new charge of the solid impure aluminum bearingmaterial for preheating that material prior to reaction with thepreheated normal halide.

In accordance with another feature of this invention, it is contemplatedthat the new charge of divided solid impure aluminum bearing material iscaused either to move continuously or at frequent intervals so that anymetallic aluminum which is deposited therein does not cause anysubstantial blockage or obstruction. This feature may be referred tobelow as movement at frequent intervals. It will be understood ofcourse, that if the material is actually moving continuously it cancertainly be said to be moving at least at frequent intervals.

A more detailed description of a preferred form of the process inaccordance with the persent invention is as follows: Normal aluminumchloride (AlCl is preheated in a gaseous state to a temperature of atleast 1000 degrees centigrade. The preheated aluminum chloride is thenpassed through divided solid impure aluminum hearing material while heatis applied to the aluminum hearing material to achieve a temperature inthe range from 1200 to 1400 degrees centigrade. At least a portion ofthe aluminum chloride reacts with the aluminum material to produce agaseous aluminum monochloride. Monochloride containing gas is thenremoved from the solid material and cooled to obtain a decompositionreaction in which the aluminum monochloride reverts to the normalaluminum chloride and releases pure aluminum. During this decompositionreaction, the temperature of the remaining gas is reduced to about 700degrees Centigrade. The decomposed gas is then passed through a newcharge of the solid impure aluminum bearing material to reduce the gastemperature to at least as low as 630 degrees centigr'ade whilepreheating the solid material to a temperature in the order of 675degrees Centigrade. The preheating step is accomplished while moving thesolid aluminum bearing material at frequent intervals so that anymetallic aluminum which is deposited in the solid material during thepreheating step does not contribute materially to blocking or impairingthe flow properties of the solid material. The direction of movement ofthe divided solid material is generally in a direction opposite to thedirection of movement of the decomposed gases therethrough. Afterpassing through the new charge of solid material, the decomposed gasesmay be recirculated and reheated and reused in the process.

For the purposes of providing a full disclosure of the process of thepresent invention, the following example typifies the practice of apreferred form of the process of the present invention:

Example I Gaseous aluminum trichloride is heated to 1200 centigrade andpassed at a rate of 20,000 pounds per hour through a body of dividedsolid impure aluminum hearing material. The divided solid impurealuminum bearing material is a crude alloy (such as obtained from acarbothermic reduction of aluminum ore, e.g. bauxite) which is suppliedat a rate of 3,860 pounds per four. As the preheated gas is passedthrough, the divided solid aluminum bearing material is heated to therange from 1200 degrees to 1400 degrees centigrade at substantiallyatmospheric pressure. A portion of the aluminum chloride then reactswith the solid aluminum material to produce a gaseous aluminummonochloride. The gases containing the monochloride are removed from thedivided solid material and substantial amounts of heat are removedtherefrom to cause a decomposition reaction in which the aluminummonochloride reverts to normal aluminum chloride and releases pureliquid aluminum at a temperature above 660 C., e.g. 680 C. or higher,and at a rate of about 2000 pounds per hour. The decomposed gases, nowat a temperature of approximately 700 degrees centigrade consist almostentirely of the normal aluminum chloride (A101 but a small amount offinely divided molten aluminum is present in suspension (aluminum fog)and an equilibrium concentration of undecomposed aluminum monochloride(AlCl) is also present. These decomposed gases are then passed through anew charge of the divided solid impure aluminum bearing material,thereby preheating the new charge to 675 degrees centigrade whilereducing the temperature of the decomposed gases to 630 degreescentigrade. With this operation, as the gases travel through theinterstices of the body of particulate charge material, the aluminum fogis thereby removed from the gases and deposited in the new charge whereit is available for later recovery in the operation of the process. Thereduction in temperature and the passage through the new charge alsorenders the gas substwtially free of the residual aluminum monochloride.

In a modified form of the process of the present invention, the sameprocess steps as described above are repeated, but after thedecomposition step the aluminum fog is mechanically separated from thedecomposed gases prior to passing the decomposed gases through the newcharge of solid impure aluminum bearing material.

The following example illustrates the practice of this modified form ofthe invention:

Example [I Gaseous aluminum trichloride is heated to 1200 degreescentigrade and passed at a rate of 20,000 pounds per hour through a bodyof divided solid impure aluminum bearing material. The divided solidimpure aluminum bearing material is a crude alloy (such as obtained froma carbothermic reduction of aluminum ore, e.g. bauxite) which issupplied at a rate of 3860 pounds per hour. As the preheated gas ispassed through, the divided solid aluminum bearing material is heated tothe range from 1200 degrees to 1400 degrees centigrade at substantiallyatmospheric pressure. A portion of the aluminum chloride then reactswith the solid aluminum material to produce a gaseous aluminummonochloride. The gases containing the monochloride are removed from thedivided solid material and substantial amounts of heat are removedtherefrom to cause a decomposition reaction in which the aluminummonochloride reverts to normal aluminum chloride and releases pureliquid aluminum at a temperature above 660 C., e.g. 680 C. or higher,and at a rate of about 2000 pounds per hour. The decomposed gases, nowat a temperature of approximately 700 degrees centigrade, consist almostentirely of the normal aluminum chloride (AlCl but a small amount offinely divided molten aluminum is present in suspension (aluminum fog)and an equilibrium concentration of undecomposed aluminum monochloride(AlCl) is also present. The decomposed gases are passed through amechanical liquid-gas separator to remove the aluminum fog, and then aportion (about 4000 pounds per hour) of the gases which have beencleansed of the aluminum fog is passed through a.

new charge of the divided solid aluminum bearing material, therebypreheating the new charge to approximately 675 degrees centigrade whilereducing the temperature of this portion of the decomposed gases toapproximately 200 degrees centigrade. The remainder (about 16,000 poundsper hour) of the decomposed gases is reheated for reuse in a repetitionof the process.

FIGURE 1 illustrates in schematic diagrammatic form the operation of thefirst embodiment of the process exemplified by Example I. FIGURE 1 alsorepresents a schematic illustration of a prefer-red apparatus which isadapted for carrying out this process. The FIGURE 1 apparatus includes,a converter 10, which is a vessel for containing the impure solidaluminum bearing material, a gas heater 12, from which heated aluminumtrichloride may be supplied to the converter 10, and a decomposer 14, inwhich the aluminum monochloride is decomposed to yield pure aluminum andaluminum trichloride. A sorubber-preheater 16 is provided which containsa new charge of the impure, aluminum bearing, divided, solid materialand through which decomposed gases from decomposer 14 are passed. Thus,the solid material is preheated and the gases are scrubbed free ofaluminum fog and residual aluminum monochloride.

An inlet 18 is provided for the introduction of the impure aluminumbearing, divided, solid material. The material then moves throughrotating gate devices 20 and 22 to the scrubber-preheater vessel 16.Details of a preferred form of the scrubber-preheater structure areshown and described below in connection with FIGURE 3. The divided solidmaterial passes from the scrubber-preheater 16 through rotating gatedevices 24 and 26 into the converter 10. After treatment in theconverter 1%, the residual solid material which has been substantiallydepleted of its aluminum content, passes out of the converter 10 throughthe rotating gate devices 28 and 30. Each of the pairs of gate devices20-22, 2426, and 2830, serve as gas locks for the purpose ofsubstantially preventing the passage of gases while providing for ameasured flow of the divided solid material.

It is to be seen from the above description that the apparatus includingthe lock formed by the gate devices 2022, the scrubber-preheater vessel16, the lock provided by the gate devices 24-26, the converter vessel10, and the lock provided by the gate devices 28410 defines a path forthe conveyance of the divided solid impure aluminum bearing materialwhile it is being processed. The material is conveyed through this pathof apparatus in sequence in the order in which the apparatus componentsare named above.

While the solid materials are in the converter 10, substantialquantities of heat must be supplied to these materials in the presenceof the aluminum halide gases in order to achieve the reaction resultingin the formation of the aluminum subhalide which combines the halogenwith the aluminum content of the solid material. This heat may beprovided by various methods, but the preferred and most satisfactorymethod which has been found is by electrical resistance heating of thesolid material. This may be accomplished simply by providing conductiveelectrodes exposed to the solid material in spaced positions within thewalls of the converter vessel, and a source of electrical energyconnected across these electrodes to provide a current between theelectrodes through the divided solid material. This method of heatingthe contents of the converter is schematically illustrated by thepresence of an alternating current generator 32 which is connected tosupply a current between the two spaced electrodes having externalterminals 34 and 36. This method of electrical heating of the converterin a subhalide conversion process for recovery of aluminum isillustrated and described in more detail in US. Patent No. 2,937,082entitled, Conversion Process for Aluminum Subhalide Distillation,"issued May 17, 1960, to A. H. Johnston, and others, and assigned to thesame assignee as the present application.

The gas heater 12 may be of conventional construction, and the normalaluminum chloride may be preheated and then supplied to the converter ata temperature in the order of twelve hundred degrees centigrade. Afterreaction within the converter 10, the gases, including both aluminummonochloride and aluminum trichloride are passed to the decomposer 14.The decomposer 14 may have various conventional constructions, however,it is preferred that it be of the splash type involving the use ofmechanical agitators to splash liquid aluminum through the gases.Furthermore, the decomposer must include means for removing substantialquantities of heat in order to successfully accomplish the decompositionreaction to release the pure aluminum. A suitable structure for thedecomposer 14 is carried out in accordance with the teachings of US.Patent 2,914,398 entitled, Recovery of Aluminum in SubhalideDistillation, and issued Nov. 24, 1959, to A. H. Johnston and F. W.Southam and assigned to the same assignee as the present application.

The operation of the decomposer 14 results in the delivery of pureliquid aluminum at the outlet 38 and in the delivery of decomposed gasesat the gas conduit 40. The conduit 40 is connected to supply thedecomposed gases to the scrubber-preheater 16. These decomposed gasesconsist mainly of the normal aluminum trichloride, but also include somealuminum fog and some aluminum monochloride. After cleaning and coolingin the scrubber-preheater 16, the gases, now almost entirely the normalaluminum chloride, pass out of the scrubberpreheater 16 to the gasconduit 42. This normal aluminum chloride from conduit 42 may berecirculated by means of a conventional circulator apparatus 44 and areturn gas conduit 46 which is connected to supply the aluminum chlorideto gas heater 12. Thus, the gas may be repeatedly recirculated andreused in the process as illustrated in FIGURE 1.

The preheating of the divided solid material in the scrubber-preheater16 by means of the decomposed gases may be all the preheating that isnecessary for carrying out the process. However, in many cases it may benecessary to supply further preheating to higher temperatures such as byusing the teachings of the US. Patent 2,937,082, previously mentionedabove.

It may be noted, in passing, that the invention in at least its broaderaspects is applicable to systems where the aluminum trichloride isultimately recirculated to the converter by procedure which partially orwholly comprises absorption or other condensation, and reevaporation,rather than by direct return of the entire i flow in the gaseous stateas shown in the drawings.

FIGURE 2 is a schematic diagram illustrating the modified process of thepresent invention as exemplified,

by Example II. FIGURE 2 also constitutes a schematic representation of asystem which is particularly adapted for carrying out this modificationof the process. The system of FIGURE 2 is similar in many respects tothe system of FIGURE 1, and corresponding components of the system ofFIGURE 2 are numbered for identification with the same numbers used forthose components in FIGURE 1. The system of FIGURE 2 includes theaddition of a mechanical separator 48, for removing entrained materialfrom a gas, which is connected by a means of conduit 40A to receive thedecomposed gases discharged from the decomposer 14. Separator 48 may bea cyclone separator of conventional construction which is operable toremove the aluminum fog from the decomposed gases, and the precipitatedliquid aluminum from this separation is discharged at the bottom outlet50 of the separator 48. The decomposed gases, after processing in theseparator 48, pass through a circulator 52, which may be of aconstruction similar to circulator 44. The output at 54, from thecirculator 52 is divided, and part of it is supplied through the conduit408 to the serubber-preheater 16 to accomplish the preheating functionof the divided solid material therein. This portion of the decomposedgas is also relieved of any residual aluminum monochloride which remainstherein. The other portion of the gas from circulator 52 is returned andrecirculated through -a branch conduit 56 to the gas heater 12A. Heater12A is substantially the same as the gas heater 12 of FIGURE 1, exceptthat it has the additional inlet for the gas conduit 56. The gas fromconduit 56 is thus reheated and reused in the operation of this system.

In the embodiment of FIGURE 2, the combined gas pressures created by thecirculators 44 and 52 are such that the gas pressure within the topportion of the converter 10 is substantially equal to the gas pressurewithin the bottom portion of the scrubber-preheater 16. Thus, the gaslock system provided in FIGURE 1 by the gates 24 and 26 between thescrubber-preheater 16 and converter 10 are not required in theembodiment of FIGURE 2, and a straight and substantially unobstructedpassage 58 is substituted. This provides an advantageous simplificationof the apparatus. It is evident that the passage 58 may be quite shortand the two vessels 16 and 10 may be practically combined.

If desired, in the process as represented by either the FIGURE 1 orFIGURE 2 embodiments, a small part of the gas from the conduit 42 may becarried for treatment in an auxiliary absorbing and re-evaporatingsystem whereby contaminating permanent gases (such as hydrogen) can beseparated so that the build up of such gases in the main system can beprevented. The re-evaporated normal aluminum halide (that is aluminumtrichloride, AlCl may then be returned to the system at conduit 46, andthus to the gas heater 12 or 12A for recirculation. Since such acleansing system for the recirculated gases is optional in the system ofthe present invention, for pur poses of clarity, it is not illustratedin the system drawings of either FIGURE 1 or FIGURE 2. However, theprovision of such a recirculated gas cleansing systems forms at least aportion of the subject matter described and claimed in a copendingpatent application Ser. No. 199,934 filed on June 4, 1962, by N. W. F.Phillips and F. W. Southam and assigned to the same assignee as thepresent application.

FIGURE 3 is a sectional side view illustrating a construction which issuitable for use as the scrubber-preheater 16 in the system of FIGURE 1or in the system of FIGURE 2. This structure includes an inlet 60 at thetop for admitting the divided solid material after passing through thegate devices 20 and 22 shown in FIGURES l and 2. The vessel 16 alsoincludes an outlet 62 at the bottom for conveying the preheated dividedsolids to the converter 10 in the systems of either FIGURE 1 or FIGURE2. While the body of solids remains in the scrubber-preheater vessel 16,as indicated at 64, heat is imparted to the solids by the decomposedgases entering at the conduit 40 and leaving at the conduit 42. Thewalls of the vessel 16 preferably include a steel outer shell 66 with asuitable refractory liner 68 preferably of a heat insulating character.The solids within the vessel 16 are preferably moved continuously, or atleast at frequent intervals if the movement is intermittent. Thismovement of solids through vessel 16 is primarily controlled by a tablefeeder 70 which is arranged for rotation on a shaft 72 at the bottom ofthe vessel 16. In order to enhance the operation of the table feeder 70,a plow member 74 is arranged within the vessel 16 and supported at afixed position above the table feeder 70 and serves to cause thematerial on the edge of the feeder to flow over the edge in response torotation thereof. The feeder 70 and the plow 74 may be of conventionalconstruction. Other similar feeder structures, such as a rotary conefeeder, may be employed if desired.

When the scrubber-preheater structure of FIGURE 3 is employed in asystem such as that of FIGURE 1, then the rotating gate members 2022 and24-26 must be operated at a rate of speed which is coordinated with thespeed of operation of the table feeder 70. As will be understood, thedimensions of a scrubber-preheater will depend on the capacity of thegiven monohalide distillation system, and particularly on the quantityof alloy to be fed through it and other conditions of operation. By wayof illustration, structure providing internal column dimensions of about1.5 to 2 feet in diameter and about 4 feet in height is one instance ofa device suitable for use in carrying out the above-described examplesof the process.

As explained above in the description of Example I, passage of the gasfrom the decomposer 14 (FIG. 1) through the aluminum-containing alloy inthe scrubberpreheater 16 renders the gas substantially free of aluminummonochloride. It' may be explained that the aluminum activity of impurealuminum-bearing material of this nature decreases with temperature, andat about 700 C. is only about 0.25. The significance here of this factis that because of absorption of aluminum into the alloy material abovethe melting point of aluminum, the gas which has passed through the bedor column of such alloy (in the scrubber-preheater) is unsaturated withrespect to pure aluminum, and therefore will not deposit aluminum onbeing cooled somewhat further, e.g. upon cooling such as might be causedby heat losses in subsequent circulation or other handling of the gas.Thus in operations such as exemplified in FIG. 1, where the entirety ofthe aluminum trichloride-containing gas from the decomposer traversesthe scrubber-preheater, there is special advantage in the foregoingrespects.

It will be understood that the examples hereinabove are illustrative andthat the process is subject to modification and variation ascircumstances or requirements may dictate in the light of its principlesas explained. F r instance, whereas in Example II conditions ofoperation have been described which involve the discharge of gas fromthe scrubber-preheater 16 at an outlet temperature of 200 C., otherconditions may be employed such as other magnitudes of flow, e.g. largerproportions of the decomposer outlet such as will afford correspondingtemperatures of gas outlet from the scrubber-preheater intermediatebetween 200 C. and say 630 C. In other words, the proportion of thetrichloride gas from the decomposer that is utilized in passage throughthe incoming impure aluminum material may be any selected value, from arather small proportion as in Example II (or even somewhat less), to theentirety of the gas as in Example I. It will also be appreciated thatapparatus embodying two circulators such as indicated at 52 and 44 inFIG. 2 (with the cyclone separator 48, if necessary) may be utilized forflow conditions such as illustrated in Example I (e.g. where all of thetrichloride gas is passed through the scrubber-preheater), if it isdesired to eliminate the lock between the latter device and theconverter, i.e. to permit use of a simple, open passage as shown at 58in FIG. 2 rather than the gates 24 and 26 in FIG. 1.

While other variations and modifications of the present invention willoccur to those who are skilled in the art, it is intended that thefollowing claims shall cover the entire valid scope of this inventionand shall include such variations and modifications.

We claim:

1. An improved subhalide distillation process for the recovery ofaluminum comprising the steps of passing a normal halide of aluminum inpreheated gaseous form through divided solid impure aluminum bearingmaterial while supplying heat thereto so that at least a portion of thegaseous halide reacts with the aluminum in the material to produce agaseous aluminum subhalide, removing the subhalide containing gas anddecomposing it at a lower temperature to obtain the reverse reaction inwhich the subhalide reverts to the normal aluminum halide and releasespure aluminum, and then passing at least a portion of the decomposedgases through a new charge of the solid impure aluminum bearing materialfor the preheating thereof prior to reaction with the preheated normalhalide.

2. The process of claim 1 in which the normal halide of aluminum is analuminum trichloride and the subhalide is aluminum monochloride.

3. The process of claim 1 in which the normal halide of aluminum is analuminum tribromide and the subhalide is aluminum monobromide.

4. An improved subhalide distillation process for the recovery ofaluminum comprising the steps of passing a normal halide of aluminum inpreheated gaseous form through divided solid impure aluminum bearingmaterial while supplying heat thereto in a temperature range above l,000C. so that at least a portion of the gaseous halide reacts with thealuminum in the material to produce a gaseous aluminum subhalide,removing the subhalide containing gas and decomposing it while removingheat therefrom to obtain the reverse reaction in which the subhalidereverts to the normal aluminum halide and releases pure aluminum, andthen further cooling the decomposed gases by passage through a newcharge of the solid impure aluminum bearing material.

5. An improved subhalide distillation process for the recovery ofaluminum comprising the steps of passing a normal halide of aluminum inpreheated gaseous form through divided solid impure aluminum bearingmaterial while supplying heat thereto so that at least a portion of thegaseous halide reacts with the aluminum in the material to produce agaseous aluminum subhalide, removing the subhalide containing gas anddecomposing it at a lower temperature to obtain the reverse reaction inwhich the subhalide reverts to the normal aluminum halide and releasespure aluminum, mechanically separating any aluminum fog entrained in thedecomposed gases, and then passing a portion of the decomposed gasesthrough a new charge of the solid impure aluminum bearing material forthe preheating thereof prior to reaction with the preheated normalhalide.

6. An improved subhalide distillation process for the recovery ofaluminum comprising the steps of preheating a normal aluminum halidesalt in a gaseous state, passing the heated aluminum halide throughdivided solid impure aluminum bearing material while supplying heatthereto to achieve a reaction in which at least a portion of thealuminum chloride reacts with the solid aluminum material to produce agaseous aluminum monochloride, removing the monochloride containing gasfrom the solid material and removing heat therefrom to obtain thereverse reaction in which the aluminum monochloride decomposes to thenormal aluminum chloride and releases pure aluminum, passing thedecomposed gas through a new charge of the solid impure aluminum bearingmaterial to thereby preheat said solid material while reducing thetemperature of said decomposed gases, said last mentioned step beingaccomplished while moving the solid material at frequent intervals, thedirection of movement of said solid material being generally opposite tothe direction of movement of the decomposed gases therethrough.

7. An improved subhalide distillation process for the recovery ofaluminum comprising the steps of preheating a normal aluminum chloridesalt in a gaseous state to a temperature of at least 1,000 degrees C.,passing the heated aluminum chloride through divided solid impurealuminum bearing material while supplying heat thereto to achieve atemperature in the range from 1000 to 1400 degrees C. so that at least aportion of the aluminum chloride reacts with the aluminum material toproduce a gaseous aluminum monochloride, removing the monochloridecontaining gas from the solid material and decomposing it while removingheat therefrom to obtain the reverse reaction in which the aluminummonochloride reverts to the normal aluminum chloride and releases purealuminum while reducing the temperature of the remaining gas to about700 degrees C., passing the decomposed gas through a new charge of thesolid impure aluminum bearing material to thereby preheat said solidmaterial to approximately 675 C. while reducing the temperature of saiddecomposed gases to at least as low as 630 C., said last mentioned stepbeing accomplished while moving the solid aluminum bearing material atfrequent intervals the direction of movement of said solid aluminumbearing material being generally in opposition to the direction ofmovement of the decomposed gases therethrough, and then recirculatingthe decomposed gases after passing through the new charge of solidmaterial to repeat the process.

8. In apparatus for subhalide refining of aluminum, in combination, arefining system comprising a preheater arranged to receivealuminum-containing charge material and having gas inlet and outletmeans, a converter connected and arranged to receive said chargematerial after preheating in said prcheater and having gas inlet andoutlet means for passage of halide gas to react with aluminum of thecharge material at high temperature, a decomposer having gas inlet andoutlet means with said gas inlet means connected with the gas outlet ofthe converter and arranged to receive reacted gas therefrom fordepositing pure aluminum metal and discharging halide gas, the gas inletmeans of said preheater being connected with the gas outlet means ofsaid decomposer to receive at least a portion of the halide gasdischarged therefrom, said preheater being operable to circulate saidhalide gas through the charge material therein to scrub said halide gasand preheat the charge material.

9. In apparatus for subhalide refining of aluminum, in combination, arefining system comprising a converter arranged to receivealuminum-containing charge material and having gas inlet and outletmeans for passage of halide gas to react with aluminum of the chargematerial at high temperature, a decomposer connected with the gas outletof the converter and arranged to receive reacted gas therefrom fordepositing aluminum metal and discharging halide gas, ascrubber-pre-heater connected to receive halide gas discharged from saiddecomposer said scrubber-preheater being arranged ahead of saidconverter in the path of said aluminum-containing charge material andcontaining a new charge of said material, said scrubber-preheater beingoperable to circulate said halide gas through said new charge to scrubsaid halide gas and preheat the new charge.

10. An aluminum recovery system comprising apparatus defining a path forthe conveyance of divided solid impure aluminum bearing material, saidpath defining apparatus including a first gas lock, a scrubber-preheatervessel, a converter vessel, and a second gas lock; said path definingcomponents being connected to receive and convey the divided solids insequence in the order named; said scrubber-preheater and said convertereach having a gas inlet and a gas outlet, a gas heater connected to saidgas inlet of said converter to supply preheated aluminum halide gasthereto, and a gas decomposer connected to said gas outlet of saidconverter to receive and decompose the gas from said converter tothereby obtain pure aluminum and including output connection means tosupply at least a portion of the decomposed gases to saidscrubber-preheater.

11. An improved system which is particularly adapted for the recovery ofaluminum by subhalide distillation comprising apparatus defining a pathfor the conveyance of divided solid impure aluminum bearing materialincluding a first gas lock, a scrub-berapreheater vessel, a second gaslock, a converter vessel, and a third gas lock; said last namedcomponents defining said path being connected to receive and convey thedivided solids in sequence in the order named; said scrubber-preheaterand said converter each having a gas inlet near the solids outlet endthereof and a gas outlet near the solids inlet end thereof, a gas heaterconnected to supply preheated aluminum halide gas to said gas inlet ofsaid converter, a gas decomposer connected between the gas outlet ofsaid converter and the gas inlet of said scrubber-preheater to receiveand decompose the gas from said converter to thereby obtain purealuminum and to supply at least a portion of the decomposed gases tosaid scrubber-preheater and a circulator connected between said gasOutlct of said scrubber-preheater and said gas heater to recirculate thegases discharged from said scrubber-preheater to said gas heater.

12. A subhalide distillation aluminum refining system comprisingapparatus defining a path for the conveyance of divided solid impurealuminum bearing material including a first gas lock, ascrubber-preheater vessel, a converter vessel, and a second gas lock;said path defining apparatus being connected to receive and convey thedivided solids in sequence in the order named; said scrubber-preheaterand said converter each having a gas inlet near the solids outlet endthereof and a gas outlet near the solids inlet end thereof, a gas heaterconnected to supply preheated aluminum halide gas to said gas inlet ofsaid converter, a gas decomposer connected to said gas outlet of saidconverter to receive and decompose the gas from said converter tothereby obtain pure aluminu-m, a mechanical liquid-gas separatorconnected to receive the decomposed gases from said decomposer andoperable to remove entrained liquid aluminum therefrom, a connectionfrom said liquid-gas separator to said scrubber-\preheater to convey atleast a portion of the decomposed gases to said scrubber-preheater.

13. A system as set forth in claim 12 which includes a circulatorconnected between said gas outlet of said scrubber-preheater and saidgas heater to recirculate at least a portion of the gases dischargedfrom said scrubber-preheater to said gas heater.

14. A system as set forth in claim 13 which includes a second circulatorconnected from said mechanical liquid-gas separator to said gas heaterto recirculate a portion of the gases discharged therefrom directly tosaid gas heater.

References Cited UNITED STATES PATENTS 2,937,082 5/1960 Johnston et al--68 X 3,078,159 2/1963 Hollingshead et a1. 75-68 X 3,220,165 11/1965Howie 7568 X 3,336,731 8/1967 Phillips et al 23-93 X 3,343,911 9/1967Eisenlohr 23-93 3,346,368 10/1967 Braunwarth et al 7568 3,351,46111/1967 Southam 75-68 HYLAND BIZOT, Primary Examiner. H. W. TARRING,Assistant Examiner.

1. AN IMPROVED SUBHALIDE DISTILLATION PROCESS FOR THE RECOVERY OFALUMINUM COMPRISING THE STEPS OF PASSING A NORMAL HALIDE OF ALUMINUM INPREHEATED GASEOUS FORM THROUGH DIVIDED SOLID IMPURE ALUMINUM BEARINGMATERIAL WHILE SUPPLYING HEAT THERETO SO THAT AT LEAST A PORTION OF THEGASEOUS HALIDE REACTS WITH THE ALUMINUM IN THE MATERIAL TO PRODUCE AGASEOUS ALUMINUM SUBHALIDE, REMOVING THE SUBHALIDE CONTAINING GAS ANDDECOMPOSING IT AT A LOWER TEMPERATURE TO OBTAIN THE REVERSE REACTION INWHICH THE SUBHALIDE REVERTS TO THE NORMAL ALUMINUM HALIDE AND RELEASEPURE ALUMINUM, AND HTEN PASSING AT LEAST A PORTION OF THE DECOMPOSEDGASES THROUGH A NEW CHARGE OF THE SOLID IMPURE ALUMINUM BEARING MATERIALFOR THE PREHEATING THEREOF PRIOR TO REACTION WITH THE PREHEATED NORMALHALIDE.
 8. IN APPARATUS FOR SUBHALIDE REFINING OF ALUMINUM, INCOMBINATION, A REFINING SYSTEM COMPRISING A PREHEATER ARRANGED TORECEIVE ALUMINUM-CONTAINING CHARGE MATERIAL AND HAVING GAS INLET ANDOUTLET MEANS, A CONVERTER CONNECTED AND ARRANGED TO RECEIVE SAID CHARGEMATERIAL AFTER PREHEATING IN SAID PREHEATER AND HAVING GAS INLET ANDOUTLET MEANS FOR PASSAGE OF HALIDE GAS TO REACT WITH ALUMINUM OF THECHARGE MATERIAL AT HIGH TEMPERATURE, A DECOMPOSER HAVING GAS INLET ANDOUTLET MEANS WITH SAID GAS INLET MEANS CONNECTED WITH THE GAS OUTLET OFTHE CONVERTER AND ARRANGED TO RECEIVE REACTED GAS THEREFROM FORDEPOSITING PURE ALUMINUM METAL AND DISCHARGING HALIDE GAS, THE GAS INLETMEANS OF SAID PREHEATER BEING CONNECTED WITH THE GAS OUTLET MEANS OFSAID DECOMPOSER TO RECEIVE AT LEAST A PORTION OF THE HALIDE GASDISCHARGED THEREFROM, SAID PREHEATER BEING OPERABLE TO CIRCULATE SAIDHALIDE GAS THROUGH THE CHARGE MATERIAL THEREIN TO SCRUB SAID HALIDE GASAND PREHEAT THE CHARGE MATERIAL.